As materials for electric parts, polyamide resins have been used that can be molded into desired shape by heat melting. In general, aliphatic polyamides such as Nylon 6 and Nylon 66 are used in many fields. These aliphatic polyamides generally have excellent moldability, but are insufficient in heat resistance under certain circumstances. Thus, for example, it may be the case that they are inappropriate as resin materials for surface-mounted components such as connectors that are exposed to high temperatures in a reflow soldering process.
On the other hand, Nylon 46, which was developed as a polyamide with high heat resistance, has the disadvantage of high water absorbency. For this reason, electric parts molded of a Nylon 46 resin composition may undergo size change due to water absorption. Moreover, when a molded article of the Nylon 46 resin composition has absorbed water and is then heated in a reflow soldering process, unwanted “blisters” occurs in the article. To avoid environmental problems, particularly in recent years, surface-mounting schemes using lead-free solders have been increasingly employed. As lead-free solders have higher melting points than conventional lead-based solders, the mounting temperature must be increased by 10-20° C. than before, making the use of Nylon 46 more and more difficult.
To overcome this problem aromatic polyamides were developed, which are the polycondensates of aromatic dicarboxylic acids (e.g., terephthalic acid) and aliphatic alkylene diamines. Aromatic polyamides have higher heat resistance and lower water absorbency than aliphatic polyamides such as Nylon 46, as well as high stiffness—a feature of polyamide resins.
However, electric parts such as connectors are becoming thinner and smaller along with the recent enhancement in the performance of cellular phones, personal computers, etc. Thus, the current challenge is to achieve higher resin fluidity upon molding and higher dimensional accuracy of a molded article (e.g., lower warpage).
To solve these problems, polyamide compositions containing a plate-shaped inorganic filler are proposed (see Patent Document 1). Plate-shaped inorganic fillers, however, significantly impair mechanical properties, particularly stiffness, of a molded article compared to glass fibers which are fibrous fillers. Accordingly, the use of such a plate-shaped inorganic filler may cause troubles in the final product. In addition, polyamide compositions containing a glass fiber having a deformed cross section are proposed (see Patent Document 2).
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-212437
Patent Document 2: Japanese Patent Application Laid-Open No. 2003-82228